Physics of auroral phenomena : proceedings of the 39th annual seminar, Apatity, 29 February-4 March, 2016 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2016. - 167 с. : ил., табл.

Evolution of rapidfluctuations of the plasma parameters during the crossing of the Earth's magnetosheath are shown by black lines in Fig. la and lb respectively. Grey line in Fig. la shows the SW ion flux measurements by Geotail located upstream from the bow shock at {30; -6; 4}GSE RE. The SW data is shifted by a plasma propagation time (-480 sec). One can see that increase of MSH ion flux toward the bow shock is likely to be due to the SW ion flux increase. Plasma flow is undisturbed except for the abrupt ion flux enhancement at 10:03-10:06 accompanied by a significant rotation of the flux vector. The flux enhancement (though significantly longer) is seen both in the SW and MSH hence it cannot be due to the magnetopause motion. We exclude time interval 10:03-10:06 UT from the study because of the polar angle value 9>25°. The angle between the interplanetary magnetic field and the bow shock normal - 0Bn- exceeds 45° during the whole interval; thus we deal with the MSH behind the quasi­ perpendicular bow shock. BS GlJ1 10° 09:30 10:00 10:30 11:00 11:30 12:00 12:30 9-Feb-2012, UT Figure 1. Evolution of parameters through the MSH: a - ion flux value in SW (grey line) and in MSH (black line); b - MSH polar angle; c-e - PSD, spectra index S2 and break frequency of the ion flux value (black line) and polar angle (grey line) fluctuations, dotted line in panel e shows the inertial length frequency; f — flatness of ion flux value fluctuations at scales 0.1, 1, 10 and 100 sec. For the further analysis we divide the interval into 142 intervals with duration of 512 sec (16 000 data points) moved away by 1 min from one another (i.e. intervals are overlapped by 252 sec). We calculate Fourier spectra at each interval. One part of the spectra can be approximated with two power laws with slopes S| and S2 separated with the break frequency Fbr: S| is close to -5/3 as predicted by Kolmogorov’s theory, S2 ranges from -4 to -2; Fbreak=0.9±0.5 Hz (Riazantseva et al., 2016). Generally, frequency spectra in the MSH as well as in the SW may be approximated in such manner. However inside the MSH another type of spectra may be observed. These spectra exhibit a broad peak at frequencies close to the break (like shown by Alexandrova et al., 2008). Thus, one can observe spectra at MHD scales (below the break) and at kinetic scales (above the break). We distinguish 3 regions inside the MSH: the middle MSH (11:00-11:20 UT), the magnetopause vicinity (09:43-10:03 UT) and the bow shock vicinity (12:04-12:24 UT). Fig. lc-e shows time evolutions of parameters of the fluctuations spectra: the power spectral density (PSD) of the ion flux value (black line here and below) and polar angle (grey line here and below) fluctuations at 2±0.1 Hz, S2 and Fbreaif Crosses in Fig le denote spectra with peak and refer to a peak frequency. All the data points in Fig. lc-e refer to a center of 512 sec intervals used for calculations. Mean values of the analyzed parameters at each location in the MSH are summarized in Table 1. PSD of the high frequency fluctuations grows toward the magnetopause and the bow shock. However, the growth rate of the PSD of ion flux value fluctuations toward the magnetopause is higher than the growth rate of PSD of the polar angle fluctuations. The slope of the ion flux value fluctuations spectra seems to be slightly smaller in the middle MSH - -3.0±0.2 - comparing to regions near the boundaries - -2.6±0.1. The slope of the high frequency part of polar angle fluctuations spectra at kinetic scales stays nearly constant across the MSH being -3.7+0.3 in the middle MSH and -3.4±0.2 near the boundaries. In the magnetopause vicinity the obtained value is well consistent with the one reported by Rezeau 67